The areal density of conventional magnetic recording media such as hard disks has been significantly improved by, for example, reducing the size of magnetic particles constituting a recording layer, changing materials, and improving the precision of head processing. Further improvements in areal density are also expected in the future. The improvements in areal density by means of conventional improvement techniques are approaching their limit, however, due to the advent of such problems as processing limits of the magnetic head, erroneous recording of information on tracks adjoining an intended track because of a spreading recording field from the magnetic head, and crosstalk during reproduction.
Discrete track media and patterned media have been proposed as promising magnetic recording media that are capable of further improvements in areal density. In these media, a recording layer is formed in a concavo-convex pattern so that the convex portions of the concavo-convex pattern serve as recording elements (for example, see Patent Literature 1). For magnetic recording media such as hard disks, the surface flatness is a significant factor in stabilizing the head flying height in order to provide favorable recording and reproducing characteristics. It is therefore desirable to deposit a filler material over the recording layer of concavo-convex pattern so as to fill the concave portions between the recording elements with the filler material, and remove an excess of the filler material above the recording layer so that the upper surfaces of the recording elements and those of the filler material are flattened.
The filler material may be deposited to fill the concave portions by using a vacuum deposition method such as sputtering. To remove the excess of the filler material for surface flattening, a dry etching method such as ion beam etching (IBE) or a polishing method such as chemical mechanical polishing (CMP) can be used.
In order to suppress the erroneous recording of information on tracks adjoining an intended track and the crosstalk during reproduction, it is preferred that the recording elements be completely divided by the concave portions between the recording elements. For example, the recording elements can be completely divided from each other by forming concave portions with sufficient depth between them.
The deeper the concave portions between the recording elements are, the thicker the filler material needs to be deposited to fill the concave portions between the recording elements. The deeper concave portions thus make the step of depositing the filler material less efficient.
The filler material is formed in a concavo-convex pattern that follows a concavo-convex pattern of the recording layer. The deeper the concave portions between the recording elements are and the greater the difference in level between the concavities and convexities of the concavo-convex pattern of the recording layer is, the greater the difference in level between the concavities and convexities on the upper surface of the deposited filler material is. In the step of flattening the upper surfaces of the recording elements and those of the filler material, the concavities and convexities on the upper surface of the filler material gradually decrease as the excess of the filler material above the recording layer is being removed. When the concave portions between the recording elements are deep and the difference in level between the concavities and convexities on the upper surface of the deposited filler material is large, the upper surfaces of the recording elements and those of the filler material fail to be sufficiently flattened unless the excess of the filler material is thick. When the concave portions between the recording elements are deep, the filler material therefore needs to be deposited accordingly thick to produce a sufficiently thick excess of the filler material. This also makes the step of depositing the filler material less efficient.
The thick excess of the filler material above the recording layer also reduces the efficiency of the step where the excess of the filler material is removed to flatten the upper surfaces of the recording elements and those of the filler material.
In short, there is the problem that the deeper the concave portions between the recording elements are, the lower the production efficiency becomes. Consequently, it seems to be preferable that the concave portions between the recording elements be formed so that the bottom surfaces of the concave portions coincide with the upper surface of the layer that lies under the recording layer.